1) Field of the Invention
The present invention relates to an ink jet recording apparatus that ejects ink and records an image on a recording medium, particularly to an ink jet recording apparatus that ejects ink droplets from a nozzle communicating with a pressure chamber by driving actuators of sidewalls partitioning the respective pressure chambers to cause the actuators to deflect so as to vary a volume of the pressure chamber.
2) Description of the Related Art
Among ink jet recording heads with which ink is ejected from a nozzle by deflecting an actuator or actuators according to a drive signal to vary the capacity of its pressure chamber, there is a shared wall type inkjet recording head in which a partition wall (sidewall) between pressure chambers serves as an actuator. In this type of recording head a time-divisional driving method is employed so that pressure chambers adjacent each other are not driven concurrently. That is, this time-divisional driving is operated such that a plurality of pressure chambers in the recording head are divided into two, three, or more groups so that neighboring pressure chambers can be driven separately at different timings from each other for ink to be ejected therefrom.
In this type of recording heads it is known that, when one pressure chamber is driven to generate a pressure vibration so as to eject ink therefrom, neighboring pressure chambers are affected so that a pressure vibration having an amplitude of half that of a pressure vibration generated in the ink-ejecting pressure chamber is derivatively produced at the same time within each of the neighboring chambers and thereby a meniscus in the respective nozzles adjacent a nozzle from which ink is ejected protrudes from the surface of the nozzle. This phenomenon remarkably appears in so-called multi-drop gradation recording in which a group of plural ink droplets that form one pixel are consecutively ejected. If the operation continues in the state as occurred in this time-divisional driving to eject ink from one of the nozzles, from the surfaces of which meniscuses protrude, a velocity of an ink droplet that is ejected from the nozzle largely drops. This results in degradation of over all recording quality.
One solution to the above problem is proposed, for example, in Japanese patent application No. 2004-42414, that in four time-divisional driving of the recording head, meniscus protrusions in nozzles occurring at successive timings of ink ejection can be suppressed by reducing amplitudes of pressure vibrations within the pressure chambers driven at the successive timings down to one forth that of pressure vibration within the ink-ejecting pressure chamber such that, when actuators associated with one selected pressure chamber are driven to eject ink therefrom, actuators relative to the respective pressure chambers adjacent the selected one, the actuators opposing ones shared by the selected chamber and one neighboring it, are also driven so as to deflect in the same respective directions as actuators, on the both sides of, driving the selected pressure chamber to deflect.
However, in the structure described in the specification, where ink ejection continues over one printing period, for example, in the case that after completion of one cycle of ink ejection from pressure chambers each being sequentially selected to be driven in one cycle of four time-divisional driving, the operation of ink ejection continues restarting from the pressure chamber assigned at the first timing division where a protrusion having occurred at the first ink ejection in the previous cycle remains as being insufficiently suppressed, the velocity of the second droplet ejected from the same pressure chamber drops significantly. This causes a problem that droplet landing positions become inconsistent.